While cathodoluminescence (CL) detectors are generally known, in conventional CL detectors using a solid-state detector as the detection element, the photodiodes are positioned inside the electron microscope vacuum chamber either on the side of the specimen or above it. A glass cover, normally coated with a very thin sputtered layer of indium-tin oxide, is therefore placed in front of the solid-state detector to reject backscattered electrons that can also contribute to the detector signal. The sputtered conductive and optically transparent thin layer on the glass is used to prevent a charging phenomenon from taking place. However, the glass cover in front of the solid-state detector can itself actually be a powerful CL emitter. This means that the glass can act as an extremely efficient converter of backscattered electrons to light which would be detected by the solid-state photodiode; however, the backscatter in prior art apparatus bears little or no relationship to the specimen under observation. Such detectors, moreover, lack portability and have generally been designed so as to be dedicated exclusively to suit the particular type of electron microscope vacuum chamber with which it is used. This invention overcomes the above mentioned drawbacks.